A postal Inspector officer and a NTSB investigator are seen through a section debris of a UPS A300 cargo plane after it crashed on approach at Birmingham-Shuttlesworth International Airport Wednesday in Birmingham, Ala. The two pilots aboard the aircraft were killed.

Federal investigators hope to find clues from the flight-data and cockpit-voice recorders pulled from the debris of a UPS cargo plane, after it slammed into a grassy Alabama hillside, killing the pilot and first officer.

Officials are “cautiously optimistic” that the recorders from the Airbus A300 – retrieved from the crash site Thursday morning – would contain “good data.” The blackened and soot-covered boxes were sent to NTSB laboratories in Washington, D.C., and officials worked through the night to recover and download the information they contained.

With data from the recorders pending, federal investigators found no early indications that mechanical problems or a precrash engine fire caused the UPS cargo plane to go down about a half mile before the runway, an NTSB official said Thursday.

Some attention is being directed toward the possibility of pilot error. The NTSB has asked the United Parcel Service to provide the agency with crew-related documents, including training records, flight schedules, and other employment records. UPS identified the victims on Thursday evening as Capt. Cerea Beal of Matthews, N.C., and First Officer Shanda Fanning of Lynchburg, Tenn.

The pilots did not send a distress signal before crashing near a north runway at the airport. The aircraft split in two upon impact.

A longer runway at Birmingham-Shuttlesworth had been closed as workers performed maintenance on the runway center-line lights. Investigators were looking into possible center-line runway light problems with the north runway, or other navigational aids associated with that runway, Mr. Sumwalt said.

Although there is no initial evidence of mechanical failure or engine fire, the UPS-owned Airbus A300 had six prior service difficulties, according to data from the Federal Aviation Administration. The most recent was in May 2012, when pilots declared an emergency after the air data computer failed during a flight.

Airbus said in a statement that it had delivered the aircraft to UPS in 2003. Since then it had flown about 6,800 flights, accumulating about 11,000 flight hours. The A300, Airbus's inaugural plane, began flying in 1972. The company manufactured a total of 816 of these planes, including the A310 model, up until 2007. The model was retired from US passenger service in 2009, according to the Associated Press.